There are many forms of coating systems in use today. One such a system is known as a continuous coater. The continuous coater is a machine which usually employs a plurality of spray coating nozzles which atomize coating material and project it onto a substrate in an effectively closed coating chamber, except for entrance and exit openings for the substrate to pass into and out of the coating zone. For coating the top side of flat stock or the like the nozzles are sometimes disposed in a horizontal circular pattern and made to rotate about a vertical axis central to the circularly disposed pattern of the spray guns. Other coaters have fixed nozzles directed at the substrate to be coated.
Not all of the coating material in these systems is deposited on the substrate due to various factors. Therefore, some coaters maintain a solvent-rich atmosphere in the coating chamber. The solvent-rich atmosphere prevents the "oversprayed" material deposited on the interior of the coating chamber from drying and forming a build up which would be difficult if not impossible to clean. Because of the solvent-rich atmosphere any coating material deposited on the walls, ceilings or floors remains in a liquid state and can be made to run into a drain and collected. Generally it can be recycled into the coating system. Any residual coating material which does adhere to the interior of the chamber can easily be washed out by means of a garden hose type solvent rinse. However, these coating systems did have disadvantages. One of these disadvantages exists in the fact that the coating material could become deposited on the interior of the coating chamber or nozzle support structure above the substrate, could collect and eventually drip onto the substrate. These drips degrade the finish.
The present invention deals with this problem of dripping. In a preferred embodiment the interior of the coating chamber is provided with a rotating ceiling section having a generally horizontally oriented outer rotating edge portion. Centrifugal force created by the rotation of the ceiling section causes the coating material deposited on it to travel to its outer rotating edge where the coating material can be thrown clear of the substrate to be coated.
In the preferred embodiment of this invention the ceiling has a central portion with a generally conically shaped underside surface sloping downwardly from the axis of rotation. The underside surface can be made to have a slope which diminishes in relation to an increase in the radial distance from the axis of rotation.
The plurality of spray coating nozzles have been advantageously mounted directly onto the rotating ceiling. Thus, as the ceiling rotates, so also do the spray nozzles rotate by means of a common drive assembly. This provides a desired coating pattern wherein each of the spray nozzles coats the substrate in an overlapping pattern with respect to adjacent nozzles due to constant movement of the substrate under the nozzles in the coating chamber. This arrangement also allows the mechanical and hydraulic hardware associated with the nozzles to be located above and be protected by the ceiling.
The ceiling is preferably made circular with a rotating diameter larger than the width of the substrate passing through the coating chamber, so as to assure that the coating material will be thrown clear of the substrate.
Troughs are provided over the entrance and exit openings. These troughs divert and carry to the side of the substrate any coating material thrown off the rotating ceiling or deposited on the side wall over the openings.
A small amount of negative pressure can be applied to the coating chamber so that a small flow of air is drawn downwardly between the outer edge of the ceiling and the side walls of the coater. This small amount of air prevents the spray droplets contained in the atmosphere of the coating chamber from entering the area above the rotating ceiling.
In another embodiment of the invention the ceiling can be made stationary although still having a downwardly sloping underside surface. In such a case any additional support structure needed for the nozzles is made to slope downwardly or at least have an underside surface which slopes downwardly off to the side of the substrate path.